Fuels refineries historically have shown considerable interest in converting crude petroleum to portable liquid fuels boiling below about 800.degree. F. Particular attention has been paid to processes which are capable of reducing the molecular weight of the heavier distillate fractions to high quality gasoline and middle distillates. Although initially a certain amount of so called thermal cracking was practised, this was supplanted almost entirely by highly effective catalytic processes that produced higher quality gasoline. At the present time practically all petroleum refiners who employ catalytic cracking depend on one version or another of a system in which the cracking catalyst is fluidized by the hyrocarbon feed and is converted while in that state. We shall for convenience collectively refer to these versions as the "fluid catalytic cracking process", or simply "the FCC process".
The outstanding feature of a modern FCC operation is that it is capable of extensively converting a clean distillate feed with minimum formation of unwanted by-products. The process is designed so that the coke by-product is carried with the catalyst and is burned in a regenator to supply necessary process heat. Economy of scale is achieved by building very large plants, typically capable of processing from about 50,000 to about 250,000 barrels per day of feed. The process, however, is not without shortcomings.
In order to restrict formation of by-products in the FCC process, it is necessary that the feed to the cracker be very low in metal content. Thus, it is current practice in almost all refineries to feed either a distillate, such as a gas oil, as the only material charged to the cracker, or predominantly a distillate together with a relatively minor quantity of other less desirable oil. This restriction on the nature of the feed is not a serious one so long as the refiner has available to him an abundant supply of a high quality crude, such as Arab Light, for instance. However, as is well known to those skilled in the art, such feeds with their large content of gas oil are becoming markedly less available, in part due to exhaustion of the supply and in part because of various other reasons. For instance, some of the significant newer finds, such as Alaska, make available crudes which are of lower quality than Arab Light. It is known that Alaskan Crude contains a relatively small fraction of gas oil and a relatively large residual oil content, making it not particularly a suitable feed for a refinery that is designed to process the better quality feeds. A second disadvantage of the FCC process is that plants must be very large in order to achieve economy of scale. As a consequence, any downtime required for maintenance or for other reason represents a significant disruption in the overall operation of the refinery, including management of the crude supply. Thus, a need has developed for processes to efficiently upgrade lower quality crudes in order to insure adequate supplies of portable liquid fuels as the availability of premium crudes declines. Most desirable would be now processes which operate at modest temperatures and low pressures, and which need not be installed on a grand scale to be economically viable.
U.S. Pat. No. 4,263,126 to Rollmann provides a method for converting waxy hydrocarbon oils to lower pour point, less viscous oils. By this method, a reactive dispersion of a zeolite such as HZSM-5 crystals is prepared with the oil to be converted, and conversion is effected by heating the dispersion. This patent is incorporated herein by reference as if fully set forth.
U.S. Pat. No. 4,282,085 to O'Rear et al. discloses extending the ZSM-5 catalyst life by dewaxing hydrodenitrogenated oils.
It is an object of this invention to provide a catalytic process for upgrading without prior hydrodenitrogenation a heavy waxy hydrocarbon oil that contains a residual oil fraction boiling above about 800.degree. F. It is a further object of this invention to provide a catalytic conversion process wherein catalyst is conserved by regeneration and recycling, and wherein a heavy hydrocarbon oil is converted in part to gasoline and distillate. It is a further object of this invention to provide a catalytic conversion process with catalyst recycle and which utilizes a small inventory of catalyst. It is a further object of this invention to provide a low-pressure catalytic process wherein a mixture of virgin and regenerated catalyst is used to upgrade a residual oil fraction. These as well as other objects will become evident to one skilled in the art on reading this entire specification including the claims appended hereto.